1. Field of the Invention
The invention relates to a stirrer for bioreactors configured, in particular, as tanks having flexible walls, comprising a plurality of articulately connected arms which are jointly rotatable about a rotational axis, wherein a first arm is disposed rotatably about the rotational axis by its first arm end on a first mounting fastened to a first side of the tank.
2. Description of the Related Art
Stirrers are an essential part of bioreactors for homogenizing temperature and concentration differences. Moreover, the stirrers prevent cell deposition in bioreactors and disperse the air or gases in aerated bioreactors.
U.S. Pat. No. 2,045,710 A discloses a stirrer for a tank. The stirrer consists of a plurality of articulately connected arms, which in the elongated state can be slid into the tank through a tank opening, whereupon some side members open outward when contact is made with the tank bottom. A first arm is rotatable, jointly with the remaining arms connected thereto, about a rotational axis. The first arm is disposed rotatably by its first arm end on a first mounting, which is fastened, in the vertical direction, to a top side of the tank.
A drawback with the known stirrer is that with its bottom two arms, in the course of rotation, the bottom side of the stirrer rubs on the tank bottom. In the case of a metal tank, this rubbing produces unwelcome particles, while in the case of a tank made of plastic sheeting, the sheeting would be damaged after a short operating time. A horizontal or oblique operation is not possible with such a stirrer.
In addition, U.S. Pat. No. 6,769,800 B1 discloses a folding baffle system or a folding deflector apparatus, which is insertable into a tank or bioreactor through an opening which is smaller than the tank diameter. The baffle arrangement is made up of a plurality of rings and longitudinal segments or arms. The longitudinal segments, following the insertion into the tank, extend as they are set down and thus can come to bear against the tank walls as baffles. During stirring with a stirrer, the baffles then act as baffle plates or flow disturbers.
This baffle apparatus is not suitable for collapsing with a suitable tank, nor should a hint of a folding stirrer be inferred from this publication.
US 2002/0105856 A1 discloses a stirrer for bioreactors configured, in particular, as tanks having flexible walls. The stirrer has a flexible stirring tube, which on two opposite reactor walls which it breaches is statically held in static seals. In order to set the stirring tube between its two fixed ends in a type of rotary motion, a relatively rigid, spirally or helically configured drive shaft is introduced into the tube.
A drawback with this is that, for the subsequent introduction of a rigid shaft, the flexible hose must have guide bushings inside it to allow, on the one hand, the drive shaft to be fed in at all and, on the other hand, sufficient play to exist in relation to the flexible tube, which latter, in the course of its “rotary movements”, is torn off or damaged at its fixed ends, which specifically cannot rotate.
The object of the present invention is therefore to provide a folding stirrer which is collapsible in a space-saving manner and can be inserted, in particular, into a tank having flexible walls.